It is common practice to recover silver in expended "hypo" photographic fixing solutions by one of three prevalently used methods: (1) chemical precipitation, (2) metallic replacement (ion displacement), (3) electrolytic plating. The latter method, to which this invention pertains, consists of flowing a direct electric current through the "hypo" solution, between electrodes, which causes the silver to be deposited in a plate form on the negative electrode (the cathode). Numerous devices to accomplish this are known. The electrolytic plating method is generally conceded to be the most desirable of the three methods, since, if the current densities are controlled and adjusted to conform to the varying concentrations of silver in the "hypo" solutions, the efficiency of silver recovery can be greater than in other methods, and, when the concentration of silver in the "hypo" solution has been lowered substantially, permits the re-cycling and re-use of the solution, thereby permitting considerable monetary savings in the purchase of photographic chemical solutions. The controlling of the current densities has, heretobefore, been accomplished manually, or, in some devices, two pre-set current levels are made available, and their use is alternated by having a simple timing device activated by the intermittent in-flow of expended "hypo" solution. Neither method provides for a close match of an appropriate current level for the constantly changing silver concentration. Insufficient levels of current density for the available silver concentration results in loss of silver recovery efficiency; excessive levels of current density for the available silver concentration causes several undesirable effects, among which are the precipitation of silver as a silver sulfide, or in more extreme disparities, the creation of a noxious gas, hydrogen sulfide. It is the object of this invention to automatically closely match the proper current density with the constantly changing silver concentrations so as to minimize or completely eliminate these effects.
A further problem which arises in systems for recovering silver from solution by electroplating is that of removing the silver from the electroplating vat. This problem is solved, according to the invention, by employing a flexible cylindrical stainless steel cathode. Silver attached to the cathode can be removed by removing the entire cathode and thereafter flexing the cathode. The cathode may be smaller in diameter than the plastic vat containing the cathode, leaving a space through which overflow of the solution may proceed. The solution is continuously rotated by means of two paddles which assures that the concentration of silver solution adjacent the cathode will not be depleted. The paddles are driven by a magnetic coupling from interiorly of the anode, which is made of graphite.